Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:

DETACHED OBJECT

The defining characteristic of detached objects is that they are, in a sense, “detached” from the rest of the Solar System.

They do orbit the Sun. They are part of the Solar System, but they keep their distance. Their orbits are so far away that they have no significant gravitational interactions with the eight known planets. As far as the detached objects are concerned, there may as well be no planets in the Solar System at all.

Hmm… Sedna and 2012 VP113 bring up a good point. While researching last week’s edition of Sciency Words, I initially thought “sednoid” and “detached object” were synonyms. But the list of known detached objects is a bit longer than the list of known sednoids.

The definition of sednoid is clear and specific: sednoids never come closer to the Sun than 75 AU. So if an object’s perihelion (point of closest approach to the Sun) were at 74.999999999 AU, that object would be disqualified from the sednoid club.

Detached objects don’t have to live with this kind of arbitrary restriction. If they stray within about 40 AU, they run the risk of gravitationally interacting with the planets. But it is that gravitational interaction that would change a detached object into some other kind of object; not the crossing of an imaginary 40 AU line in space.

Sednoids and detached objects are so new to our knowledge of the Solar System that the terminology is still evolving. You could choose to think of sednoids and detached objects as distinctly different groups, or you could think of sednoids as a subset within the larger population of detached objects.

It’s also possible that as we learn more about the Oort cloud (the existence of which has not yet been observationally confirmed) and the Ninth Planet (the existence of which has not yet been observationally confirmed), we may abandon this terminology in favor of new names that make more sense.

So in a distant Sci-Fi future when humanity ventures out beyond the orbit of Neptune to explore these strange objects and harvest their resources, perhaps we’ll invent some new sciency words that better describe them.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:

SEDNOID

There are currently only two known sednoids. The first is Sedna (from which the word sednoid is derived). The other is named 2012 VP113 (or “Veep,” as I like to call it).

A possible third sednoid was discovered in late 2015. It has the fun, easy-to-remember name V774104. It may take a while for astronomers to determine V774104’s orbital path. It will take a bit longer for them to think up better names.

There’s a lot of ongoing debate over what exactly these two (or three) objects are. They might be former Kuiper belt objects, or they might be part of the Oort cloud, or they may even be objects captured from other star systems.

For our purposes, the defining characteristic of sednoids is that they keep their distance from the rest of the Solar System, coming no closer to the Sun than 75 AU. For the sake of comparison, Neptune orbits the Sun at a distance of approximately 30 AU, and the Kuiper belt terminates at a distance of about 50 AU.

This means sednoids are so distant that they don’t have any significant gravitational interactions with the eight known planets. As far as Sedna and Veep are aware, there may as well be no planets in the Solar System at all.

Okay, the orbits of both Sedna and Veep are a little too strange. They’re too eccentric. Way too eccentric.

At perihelion (closest approach to the Sun), Veep is approximately 80 AU away; at aphelion (farthest distance from the Sun), Veep is over 400 AU away. Sedna’s orbit is even crazier, with perihelion at 75 AU and aphelion at a distance of over 900 AU!

It’s hard to believe the sednoids ended up in these bizarre orbits on their own, so they must have had gravitational interactions with something. If the eight known planets couldn’t have influenced the sednoids, does that mean there’s another planet out there? Could the elusive and controversial Planet X be responsible for these weird orbits?

Assuming Planet X exists at all.

P.S.: I’ve been highly skeptical of the whole Planet X thing, or as it is now being called the Ninth Planet hypothesis. However, after yesterday’s post on the clustering of scattered disk objects and today’s post on sednoids, I have to admit that something odd seems to be going on beyond Neptune’s orbit.